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Radiofrequency ablation with an irrigation catheter is available to ablate ventricular tachycardia in cases with a structural heart disease. The “pop phenomenon” associated with the use of this system remains crucial but direct visualisation of the “pop phenomenon” has not been reported. A deflectable 8.5 MHz phased array intracardiac echocardiography (ICE) catheter (Acu Nav, Acuson Inc) presented in a canine model the visual aspect of a real time “pop phenomenon” on the apical posterior wall of the left ventricle in vivo. Using a temperature controlled system, low power energy was delivered to the left ventricle for 45 seconds. The mean temperature was 55°C with a mean power of 25 W. Suddenly, the ablated lesions were vividly demonstrated by the presence of a notable increase in tissue density and the central hypoechoic area (below left). Simultaneously, we found a bubble formation in the left ventricle. The real time measurements of the maximum width and depth of the hyperechoic lesion and the central hypoechoic area were 13.8 and 9.0 mm, and 6.1 and 4.5 mm, respectively. A histological examination revealed sharply demarcated ablated lesions and a central crater formation (below right). Macroscopically, the maximum width and depth of the ablated lesion and the central crater were 13.2 and 8.8 mm, and 6.2 and 4.7 mm, respectively. The sizes of the ablated lesion and the crater on ICE corresponded to those of the macroscopic measurements.
Phased array ICE may be useful in the direct identification of an ablated lesion and crater formation when a “pop phenomenon” occurs during low power ablation.